[Top][All Lists]
[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [Qemu-devel] [libvirt] [PATCH v2 3/3] qemu-config: Add new -add-fd c
From: |
Eric Blake |
Subject: |
Re: [Qemu-devel] [libvirt] [PATCH v2 3/3] qemu-config: Add new -add-fd command line option |
Date: |
Thu, 11 Oct 2012 10:04:04 -0600 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:15.0) Gecko/20120911 Thunderbird/15.0.1 |
On 10/10/2012 04:31 PM, Eric Blake wrote:
> Another missing validation check is for duplicate use. With the monitor
> command, you ALWAYS have a unique fd (thanks to SCM_RIGHTS). But with
> the command line, I can type 'qemu -add-fd fd=4,set=1 -add-fd
> fd=4,set=2'. Oops - I've now corrupted your set layout, unless you
> validate that every fd requested in -add-fd does not already reside in
> any existing set.
>
> Thinking aloud:
> On the other hand, being able to pass in one fd to multiple sets MIGHT
> be useful; in the SCM_RIGHTS monitor command case, I can pass the same
> fd from the management perspective into multiple sets, even though in
> qemu's perspective, there will be multiple fds created (one per call).
> Perhaps instead of directly adding the inherited fd to a set, and having
> to then sweep all sets to check for duplicates, it might make sense to
> add dup(fd) to a set, so that if I call:
>
> qemu -add-fd fd=4,set=1 -add-fd fd=4,set=2 -add-fd fd=5,set=2
>
> what REALLY happens is that qemu adds dup(4)==6 to set 1, dup(4)==7 to
> set 2, and dup(5)==8 to set 3. Then, after all ALL -add-fd have been
> processed, qemu then does another pass through them calling close(4) and
> close(5) (to avoid holding the original fds open indefinitely if the
> corresponding sets are discarded).
Another idea: a hybrid approach - the _first_ -add-fd 4 directly adds 4
to the set, all other -add-fd 4 end up adding dup(4) instead (well,
fcntl(F_DUPFD_CLOEXEC), but you get the picture). That is, do the
duplicate scanning, and if there is no duplicate, use the fd directly;
if there IS a duplicate, then put a unique fd number as a copy into the
remaining sets. That way, you don't have to do a final close() sweep
across the -add-fd arguments passed on the command line, and you still
don't have to worry about duplicated fds across multiple sets causing
mayhem in qemu_close().
--
Eric Blake address@hidden +1-919-301-3266
Libvirt virtualization library http://libvirt.org
signature.asc
Description: OpenPGP digital signature
- Re: [Qemu-devel] [PATCH v2 2/3] monitor: Enable adding an inherited fd to an fd set, (continued)
[Qemu-devel] [PATCH v2 1/3] monitor: Allow add-fd to any specified fd set, Corey Bryant, 2012/10/10
[Qemu-devel] [PATCH v2 3/3] qemu-config: Add new -add-fd command line option, Corey Bryant, 2012/10/10
Re: [Qemu-devel] [libvirt] [PATCH v2 3/3] qemu-config: Add new -add-fd command line option,
Eric Blake <=
Re: [Qemu-devel] [libvirt] [PATCH v2 3/3] qemu-config: Add new -add-fd command line option, Eric Blake, 2012/10/11
Re: [Qemu-devel] [libvirt] [PATCH v2 3/3] qemu-config: Add new -add-fd command line option, Corey Bryant, 2012/10/11